1. Field of the Invention
Embodiments of this invention relate to methods for producing fluids from subterranean formations through the formation of a network of proppant pillars, clusters, columns, or islands in fractures in a formation during and/or after formation fracturing, proppant networks, and proppant pillars.
More particularly, embodiments of this invention relate to methods for producing fluids from subterranean formations through the formation of a network of proppant pillars, clusters, columns, or islands in fractures in a formation during and/or after formation fracturing, proppant networks, and proppant pillars, where the methods include a sequence of proppant stages designed to form proppant networks and proppant pillars that increase fracture conductivity.
2. Description of the Related Art
During fracturing applications, proppants are deposited in the fracture with the aid of fracturing fluid to keep the fracture opened. Generally proppant particles are placed in the fracture in concentrations sufficient to form a tight pack. When fractures close under pressure, this closure causes compaction, resulting in some of the proppant crushing or proppant embedment into the fracture face. Both phenomena results in restricted flow paths through the fracture stimulated volume and hence causes decreased fracture conductivity. The porosity of the pack decreases even more if the proppants are not of high strength, spherical or larger in size. Higher formation pressure also leads to decreased fracture conductivity.
Historically, many techniques have been proposed to get high conductivity fracture. For example, one techniques involves depositing low volume of proppant in the fractures and creating a “partial monolayer” to generate high conductivity. Proppants are placed far from each other, but are still able to keep fractures opened. Fluid flow around widely spaced proppants. This is practiced by Halliburton using plastic proppants and Baker Hughes using light weight or ultra-light weight proppants, for example, walnut hull. For another example, Schlumberger used channel hydraulic fracturing technique also called “HiWay” frac to create open pathways within the proppant pack, by intermittently pumped slugs of proppants during fracturing with fibers to form islands of proppants or pillars in the fractures. The engineered channels provide highly conductive paths for flow of fluids in the fractured formation. For another example, Halliburton described using proppants coated with adhesive substance at lower concentration to make the higher conductivity fractures. For yet another example, Halliburton described introducing degradable materials in the proppant pack, which over time degrade to provide higher porosity fractures. Many other techniques to form high porosity fractures has also been proposed, used or introduced.
While many inventions have been used to achieve high conductivity fractures that have a reduced tendency to collapse under high pressure production conditions, the present invention describes methods to create high conductivity fracture by increasing porosity using zeta potential altering chemistries and proppants introduced under fracturing conditions, where the conditions are sufficient to produce proppant pillars within a fractured formation through sequences of injections of different fracturing fluids into a formation some including no proppant and no aggregating or zeta altering compositions, some including no proppant, but aggregating or zeta altering compositions, and some including both proppants and aggregating or zeta altering compositions.